From Ryzom Wiki

Nexus is considered the heart of the new lands and is the only region of the Nexus Minor continent. As the name implies it is a place where many things come together and indeed most of the Prime Roots regions have portals leading to Nexus. In fact there is no other way to get to Nexus other than through the Prime Roots.

Nexus is a PvP region. The region is of the forest ecosystem but materials harvested here will be of General Ecosystem like Prime Roots materials. The creatures here are all forest creatures.